Many products require an optical system that is capable of spreading light over a large area and controlling the direction of the light as it exits the system. Recent improvements in the performance of LEDs, coupled with a concurrent reduction in the cost of their production, have made LEDs a more viable option for many applications. However, many applications such as LCD backlights, signs with backlights, overhead lighting, and automotive lighting require the concentrated light that is generated by an LED to be spread over a large area, while still controlling the direction of the light. These applications would benefit from an improved optic system to provide the desired light control.
A historic advancement in controlling light output from energy saving lighting fixtures was made by Donald Phillips, et al, for the “Low Brightness Louver” disclosed in U.S. Pat. No. 2,971,083, issued Feb. 7, 1961. This invention allowed for the practical use of fluorescent light fixtures in workplaces. The Phillips device provided a cost-effective implementation of fluorescent lamps that produced a light output distribution that was acceptable for the office environment. The utilization of the Phillips louver has saved an incredible amount of energy over the years. However, with the mass implementation of fluorescent fixtures came mass consumption of fluorescent lamps. Disposal of expended fluorescent lamps has become a big environmental problem due to the fact that mercury is required for use in the fluorescent tubes, and disposal of mercury has a large environmental impact. The environmental issue and other disadvantages inherent to fluorescent lighting have led to the prospective development of LEDs as an alternative lighting source.
The backlighting for LCD devices is an area in which compact optic systems have seen significant developments which are being extended to other lighting systems. Three groups of prior art references have addressed the control of light in LCD type displays. Among these, prism type brightness enhancing films (BEFs) comprise the most common class. One example of a BEF device is U.S. Pat. No. 5,467,208, “Liquid Crystal Display” by Shozo Kokawa, et al., issued Nov. 14, 1995. This reference discusses the prior art of prism type films and discloses improvements to the art. One drawback to prism films is that they have only limited control of the angle of the light output. Further, changes to the prism features result in only slight variations in the light output. The prism films are also limited to an essentially two dimensional structure. If an application requires control of the light in two directions, two BEFs must be deployed.
A second class of prior art is exemplified by U.S. Pat. No. 6,421,103, “Liquid Crystal Display Apparatus . . . ” by Akira Yamaguchi, issued Jul. 16, 2002. The Yamaguchi reference discloses another device to control light as it enters an LCD panel. The patent discloses light sources, a substrate (not used as a light pipe), apertures, and reflective regions on the substrate. Light directed to the substrate is either reflected by the reflective surface or passed through the apertures. The light that passes through the apertures is then captured by a lens that is used to control the direction of the output light. Yamaguchi teaches restriction of the angle of the output light to concentrate more light directly at the viewer of an LCD type display. The Yamaguchi device provides much greater control of the output light than can be had with a BEF device. But a drawback to the Yamaguchi device is that it is extremely inefficient. Light is reflected off of the reflective surface many times before it passes through an aperture. Even when the reflective surface is made with a high reflectance material, the losses in intensity are substantial. Therefore while the control of light with a Yamaguchi type device is superior to that of BEF devices, the efficiency of the device is very low.
U.S. Pat. No. 5,396,350, “Backlighting Apparatus . . . ” by Karl Beeson, issued Mar. 7, 1995; and U.S. Pat. No. 7,345,824, Light Collimating Device” by Neil Lubart, issued Mar. 18, 2008; disclose devices in the third class of prior art light control optics for LED light source devices. The Beeson and Lubart references disclose a reflective structure on the viewer side of the light pipe. The range of control of these reflective structures is limited, and the control is not equivalent to that provided by devices such as Yamaguchi. Further, the reflective structures of the Beeson, Lubart type devices are positioned very close to the LCD panel. The close positioning allows any defects in the output of the reflective structures to be easily seen by the viewer of the display.
Still another method of collection and control of light from LEDs is accomplished with the use of a conventional reflector and refractive optics in combination. A typical example of this type of system, currently state of the art, is shown in FIG. 1. Although this type of system is effective in collecting all of the light from the LED, the ability to control the output is limited. The light that is collected by the reflector portion of the system has a generally uniform cone angle as it leaves the reflector. In this example the cone angle ranges from 3.9 degrees to 4.5 degrees. The refractive optics (i.e. the light transmitted through the lens) has a much greater cone angle, 41 degrees. Therefore if a particular application requires a cone angle of less than 41 degrees, this system cannot be used.
Another drawback inherent to the system of FIG. 1 is due to the fact that the output light comes from two sources, a lens and a reflector. The nature of the light from the lens is quite different than that from the reflector. It is therefore very difficult to optimize the output from both sources simultaneously. Measures that have a positive effect on the light output from the lens tend to have a negative effect on the light output from the reflector, and vice versa.
Accordingly, it is an object of the present invention to provide an optical system that is extremely efficient and also provides excellent control of the output light, all of the output light coming from a single type of source within the system.
It is another object of the present invention to provide a less complex optical system than is used in current art systems, thereby reducing the cost to manufacture the device.
It is another object of the present invention to have accurate control of the output beam angle and the distribution of the illuminant within the beam.
It is a further object of the present invention to provide a light pipe that will provide accurate control of the direction of light output.